ITU-T H.264/MPEG-4 part 10 is a recent international video coding standard, developed by Joint Video Team (JVT) formed from experts of International Telecommunications Union Telecommunication Standardization Sector (ITU-T) Video Coding Experts Group (VCEG) and International Organization for Standardization (ISO) Moving Picture Experts Group (MPEG). ITU-T H.264/MPEG-4 part 10 is also referred to as MPEG-4 AVC (Advanced Video Coding). MPEG-4 AVC achieves data compression by utilizing the advanced coding tools, such as spatial and temporal prediction, blocks of variable sizes, multiple references, integer transform blended with quantization operation, entropy coding, etc. MPEG-4 AVC supports adaptive frame and field coding at picture level. MPEG-4 AVC is able to encode pictures at lower bit rates than older standards but maintain at least the same quality of the picture.
Rate control is an engine that dynamically adjusts encoding parameters so that the resulting compressed bit rate can meet a target bit rate. Rate control is important to regulate the encoded bit stream to satisfy the channel condition and to enhance the reconstructed video quality. However, in actuality, single-pass rate control for an MPEG-4 AVC often results in uneven quality within a picture as well as from picture to picture. For example, there may be serious pulsing problems around instantaneous decoding refresh (IDR) picture of MPEG-4 AVC with single-pass rate control. Many of the causes of the uneven quality result from the inability to accurately estimate a target bit rate for future pictures that have yet to be encoded in the stream.
Additionally, in instances where a target bit rate is estimated, a further difficulty may arise in controlling the actual bit rate to achieve the target bit rate. The inability to control the bit rate may affect buffers in encoders used to encode the bit stream.